The present invention relates to an engine.
In particular, the invention relates to an internal or external combustion engine that employs purely or predominantly rotational members.
The majority of internal combustion engines in use today employ reciprocating pistons. However, it is recognised that the presence of reciprocating components imposes a limit upon the maximum speed of operation of an engine. Moreover, the need to contain the forces associated with reciprocating components mandates the use of components of substantial weight. For this reason, attempts have been made to devise engines that employ components having purely or predominantly rotary components. To date, the most successful rotary piston engine is the xe2x80x9cWankelxe2x80x9d engine, named after its German inventor. However, this unit although simple, has had limited commercial success due to several reasons. The foremost of these is its reputation for suffering from sealing problems, followed by low torque at low engine speed, fuel inefficiency and relatively high pollution levels. The unit also suffers from the need for careful maintenance and its speed of operation must be limited, if seal failure is to be avoided. Moreover, the piston of a Wankel engine (at least, of the type most commonly used in practice) undergoes motion that is not purely rotary; it also has an oscillatory component, and this leads to residual vibration.
Gas turbine engines are also known. In such engines, expanding combustion gas is caused to impinge upon blades of a rotor, and thereby impart a torque to the rotor. A gas turbine has the advantage that its rotor undergoes purely rotational motion, and it can therefore operate at high speed with a minimum of vibration. However, such engines typically operate efficiently only within a relatively narrow band of engine speeds which renders them unsuited to operation in many circumstances, a most important example of which is as an engine for a motor road vehicle.
An aim of the invention is to provide an engine that has predominantly rotary components, and which overcomes or at least ameliorates some disadvantages of known engines.
From a first aspect, the invention provides an engine including a combustion assembly comprising a rotor and a stator, in which a combustion chamber is defined in the stator and a fluid receiving chamber is defined in the rotor, in which combustion gas can expand from the combustion chamber into the receiving chamber, whereby momentum is transferred from the combustion gas to the rotor.
Such an engine may be embodied with a minimum of components, none of which undergo oscillatory movement.
Such an engine may typically have a plurality of rotor expansion chambers into which combustion gas can expand in turn. Most commonly, the rotor expansion chambers are of different volumes. In particular, the rotor expansion chambers are typically of successively increasing volumes. The combustion chamber is advantageously of volume larger than several of the rotor expansion chambers.
In preferred embodiments, the stator has a plurality of stator expansion chambers into which gas can expand from the chambers of the rotor. Typically, the rotor expansion chambers are of different volumes. In particular, the rotor expansion chambers may be of successively increasing volumes.
In preferred embodiments the rotor has a transfer chamber through which combustion gas can pass into the combustion chamber during a portion of the rotation of the rotor.
An engine embodying the invention may be provided with spark ignition apparatus in association with the combustion chamber for igniting a charge of combustible fluid received therein. Typically, the ignition apparatus includes a spark plug.
In an engine embodying the invention, either one or both of the rotor and stator may be formed from a material that has self-lubricating properties. For example, either the rotor or the stator may be formed from spheroidal graphite iron.
Alternatively or additionally, an engine embodying the invention may have an oil mist injector operative to inject an oil mist into a space between the rotor and the stator. Typically, such an oil mist is injected at a position in advance of the combustion chamber.
An engine embodying the invention may, moreover, have a lubricating brush to add lubricating material such as graphite between the stator and the rotor.
In one class of embodiments of an engine, the rotor is shaped as a disc having chambers opening to the periphery of the disc. In such embodiments, the engine preferably has a gap control system for controlling a separation between the rotor and the stator during operation of the engine. Such a gap control system may operate to move the stator radially with respect to the rotor.
In such embodiments, the rotor may comprise a rotor assembly that includes a rotor casting. The rotor casting may be shaped as a disc, having peripheral openings into voids formed therein. The rotor assembly may further comprise end plates secured to the rotor casting to close these voids axially. Several such rotor castings may be assembled together between endplates to provide a combustion assembly of greater combustion capacity, giving rise to a convenient modular form of construction.
In embodiments according to the last-preceding sentence, a spacer may be disposed between adjacent rotor castings to aid in removal of heat from the combustion assembly, and from the rotor castings in particular. The spacer may typically include a through passage in alignment with cooling fluid ducts of the rotor castings.
The stator assemblies may likewise comprise a stator assembly that includes a stator casting. The stator casting may be shaped as a to partially surround the rotor assembly, having openings into voids formed therein. The stator assembly may further comprise end plates secured to the stator casting to close these voids axially. Several such stator castings may be assembled together between endplates to provide a combustion assembly of greater combustion capacity.
In embodiments according to the last-preceding sentence, a spacer may be disposed between adjacent stator castings to aid in removal of heat from the combustion assembly, and from the stator castings in particular. Such a spacer may be formed with holes to link the combustion chambers of the various stator castings in an axial direction. Alternatively, or additionally, combustion mixture may be introduced into each of the combustion chambers.
The optional rotor and/or stator spacer may be provided with fins to remove heat therefrom.
In another class of embodiments, of an engine, the rotor is shaped as a frustum, having chambers opening to its periphery. In such embodiments, the stator typically partially surrounds the rotor. Such embodiments may have a gap control system for controlling a separation between the rotor and the stator during operation of the engine. The gap control system may operate to move the stator axially with respect to the rotor.
In embodiments including a gap control system, the gap control system may include a non-contact sensor. Such a sensor may operate by capacitive sensing, inductive sensing or a combination of capacitive and inductive sensing.
In yet another class of embodiments, the stator are both disc shaped, the combustion chamber being defined between flat faces of the rotor and the stator. In such embodiments, a gap control typically operates to move the stator axially with respect to the rotor.
In embodiments according to either of the last two preceding paragraphs, the rotor and/or the stator may comprise a casting and one or more endplates, as described above.
An engine embodying the invention may further include a compressor for supplying combustion air to the combustion assembly. The compressor may be driven by the rotor. In a convenient construction, the compressor and the rotor may be carried on a common shaft or upon interconnected coaxial shafts. Preferably, an intercooler is disposed between the compressor and the combustion assembly operative to remove heat from the combustion air, and thereby improve volumetric efficiency of the engine.
For spark ignition embodiments, the compressor may deliver combustion air at a pressure in the range of 4 to 7 Bar. Where combustion air charge cooling is provided (for example, in the form of an intercooler) this pressure may be increased to a range of 6 to 12 Bar. In compression-ignition embodiments, the pressure may typically be in the range of 9 to 15 Bar. Where combustion air charge cooling is provided (for example, in the form of an intercooler) this pressure may be increased to a range of 20 to 30 Bar.
In some embodiments, fuel is injected into a stream of combustion air externally of the combustion assembly. Alternatively or additionally, fuel may be injected into a chamber within the combustion assembly.
In addition to fuel and air, water may be introduced into the combustion chamber together with air and fuel. In some of such embodiments, the water may expand as vapour, during combustion, the water vaporises and expands into the receiving chamber and transfers at least some of its momentum to the rotor.
From another aspect, the invention provides a combustion engine including a rotor and a stator, said stator carrying a first set of combustion chambers and said rotor carrying a second set of combustion chambers, the arrangement being such that during operation said rotor rotates relative to said stator and a working fluid is transferred in succession between the combustion chambers of said first and second sets, thereby driving the rotation of the rotor.
By means of this arrangement, the engine can be provided with combustion chambers of a shape and size optimised for a particular intended application. Moreover, the rotor is typically arranged such that its motion is purely rotational, with no oscillatory component.
Important to this engine""s success is a novel thermodynamic cycle that is employed in the xe2x80x98hotxe2x80x99 portion of the unit. The engine may have either a single or multistage separate compressor section to achieve compression of the working fluid, which is normally air.
According to a further aspect of the present invention there is provided a combustion engine including a rotor and a stator, said stator carrying a first set of combustion chambers and said rotor carrying a second set of combustion chambers, the arrangement being such that during operation said rotor rotates relative to said stator and a working fluid is transferred in succession between the combustion chambers of said first and second sets, thereby driving the rotation of the rotor.
Advantageously, one or more types of combustion chamber are provided, including one or more of the types referred to hereinafter as xe2x80x98motherxe2x80x99, xe2x80x98maidxe2x80x99 and xe2x80x98daughterxe2x80x99 chambers.
Advantageously, the rotor and/or the stator include a set of daughter chambers that increase progressively in volume.
At least some of the chambers are preferably retort-shaped.
The working fluid is preferably transferred between the chambers by a process referred to hereinafter by the term xe2x80x9cHarmonic Gas Fluctuationsxe2x80x9d.
Advantageously, the engine includes a compressor for supplying a combustible mixture of fuel and air to the combustion chambers.
According to a further aspect of the invention there is provided a combustion engine including a rotor and a stator, said engine employing a cadence-recursive expansion process for driving the rotation of the rotor. The cadence-recursive expansion process is described in more detail below.
An engine embodying this invention may be designed to be reliable and may avoid sealing problems by virtue of its high speed of operation and specific design features. It may not suffer from pollution effects or low torque levels. It may also be extremely simple, having (at least theoretically) just one rotating part in its simplest embodiment. Moreover, an engine embodying the invention may have an extremely high specific power output level with low weight, thus providing a power to weight ratio of the same order as the most efficient gas turbines currently available. The output of an engine embodying the invention is typically principally shaft power, not thrust as in a gas turbine unit. Hence it may be suitable to be used for prime moving applications, ranging from all types of road transport to all types of aeronautical applications, including helicopters and VTOL aircraft. It may also be suitable for static power generation, co-generation and marine applications. Due to the combination of rotary action and the unique thermodynamic cycle employed it may be fuel-efficient and because of its extreme simplicity in principle, it may be inexpensive to manufacture.
Throughout this application, comparisons are drawn with comparable reciprocating designs to illustrate points being discussed.